Paper backed adhesive tape



United States PatentOfiice 2,726,957 Patented Dec. 13, 1955 PAPER BACKEDADHESIVE TAPE Laszlo Walter Eger, East Hampton, Conn, and Edward WilliamEngel, New Brunswick, N. 5., assignors to Permacel Tape Corporation, acorporation of New Jersey No Drawing. Continuation of application SerialNo. 556,494, September 29, 1944. This application October 23, 1948,Serial No. 56,258

Claims. (Cl. 117-76) This invention relates to flexible, non-Wovenfibrous sheeting impregnated with a butadiene copolymer deposited fromaqueous dispersion to improve internal strength and to impart to thesheet a high degree of nonhygroscopicity. The invention also relates tothe combination of such sheeting with a coating of normally adhesivematerial, i. e., to a pressure-sensitive adhesive tape.

The internal strength of the improved sheet is insured by the bondingtogether of the fibers in the sheet in such manner that the sheetingwill possess high tensile strength and not split into laminations ordelaminate even though relatively large forces are applied tending toseparate the fibers. Non-hygroscopicity results from the nature of theimpregnant and the extent to which it is introduced into the sheet.

Pursuant to the invention, a flexible, porous, fibrous web, such aspaper, which consists of matted fibers, or unwoven fibrous sheeting suchas that manufactured by the Chicopee Manufacturing Corporation and soldunder the trade name Masslinn, or other highly porous fibrous websselected according to the intended use, is impregnated with aconcentrated aqueous dispersion of a copolymer of butadiene and anunsaturated compound in which the solid particles of the dispersion arepreferably less than 4 microns in diameter. The preferred unsaturatedcompounds are mono-unsaturated compounds, and may be aromatic, such asstyrene, or aliphatic, such as the unsaturated nitriles (e. g., acrylicnitrile, alpha-methacrylic nitrile, alpha-ethacrylic nitrile,alpha-isopropylacrylic nitrile), isobutylene, and methacrylates such asmethyl methacrylates, their equivalents, and homologs. For convenience,wherever reference hereinafter is made to copolymers of butadiene andstyrene, it should be understood, unless otherwise noted, that theintention is to include within the scope of these terms, the other copolymers of butadiene that have been mentioned. The limitation in thesize of the solids particles in the dispersion is to insure that theparticles will enter the pores of the fibrous Web. With most sheetingsuitable for practising the invention, this will occur if the particlesare predominantly less than 4 microns in diameter.

The flexible sheet when treated preferably should be saturated, i. e.,it should include as much impregnant solids as possible, ordinar ly tothe extent of between 49 to 60 percent of the total weight of the sheet.Saturation to this degree may be obtained by using an aqueous dispersionhaving a solids content comprising approximately 30 to 60 percent byweight, selected concentration dependin' upon the characteristics of theporous Web. in other words, the solids content in the dispersion is madelarger according to the greater ability of the sheet to absorb solids.

The improved product possesses many advantages from the standpoint ofmanufacture and use. Impregnant preparation is simplified. The use ofundesirable, inflammable and toxic solvents is eliminated. Vulcanizingor curing steps are unnecessary. The product is extremely soft andpliable. It has high tensile strength and great resistance to fiberseparation. Thin sheets of the impregnated web are very translucent. Thecolor is light, although, by the simple addition of coloring agents tothe original web or to the impregnant, various attractively coloredsheets may be obtained. Furthermore, the improved sheet has goodelongation and has relatively high porcs 'y, co bined with goodresistance to those comsoiv its with which it is most apt to come incontact in normal industrial use.

The sheets are well bonded internally and therefore are particularlysuitable for protective packaging or in conjunction with normallyadhesive material as a backing or interliner for adhesive tapes, or inthe printing industry Where tacky printing inks have a tendency toresist the separation of stacked sheets. As a backing for apressure-sensitive adhesive tape, the sheet will withstand, withoutsplitting or delamination, the sudden and forceful removal of the tapefrom surfaces to which it has adhered, enabling the tape to be used overand over again. it has been found, too, that the application ofpressuresensitive adhesives to the improved sheet seldom requires aprimer to anchor the adhesive to the backing and that backsize may beavoided with many adhesives customarily used. Several costlymanufacturing steps are thus eliminated when using the improved sheetingas the backing for a pressure-sensitive adhesive tape.

The improved sheeting gives satisfactory service even after long storageor under extremes of climatic conditions where other considerably moreexpensive products have failed. it may be used to great advantage ininstances where very high or very low temperatures are encountered. Byway of example, it will retain its internal and tensile strength andwill stay flexible, even after prolonged exposure to temperatures above300 F. Tests have shown that after exposure to this temperature for fourand a half hours, the sheet encounters no change of properties exceptfor slight discoloration. At F. and below the sheet performs tosatisfaction the same as at normal temperatures.

From what has been said, it is manifest that there has been produced asheet having many applications which hitherto were barred to the use ofinternally bonded, fibrous, non-hygroscopic sheets. For instance, in theform of a backing for normally adhesive tapes and in other forms asWell, the product can be used in the aircraft, automotive, typewriter,and other machine industries to mask parts during application and hightemperature treatment of baked finishes and enamels. The sheets willperform equally well in similar masking operations in finishingelectrical, radio, and electronic equipment. The ability of the sheet toresist cold is of great importance in connection with aircraft designedfor high altitude fiying, and in the locker industry for packaging foodsand other perishables for long storage at low temperatures.

While the foregoing advantages may be obtained using standard butadienestyrene copolymers as the impregnant for the sheet, the surprisingdiscovery has been made that the tensile and internal strength is vastlyimproved if butadiene styrene copolymers are used having a higher thanconventional ratio of styrene to butadiene. l-leretofore, the usuallyavailable butadiene styrene copolymers, such as Buna S or GRS had astyrene content of about only percent by weight. In so far as thisinvention is concerned, however, it is preferred that the styrenecontent of the butadienne styrene copolymer range between and percent byWeight. The increased olefin content reduces the elastic properties andimproves the plastic properties of the copolymer, thereby rendering thecopolymer-substantially superior as an impregnant for fibrous sheeting.

Most commercial latices of this general type, i. e. aqueous dispersionsof butadiene styrene copolymers, are

invention will likewise prolong. the life of the resultant product. Forinstance, there is contained in one creamed latex made by a domesticsource of supply and which has been found satisfactory from /2 topercent (based Creamed dispersions of butadiene styrene copolymersuitable for practising the invention may be obtained commercially. Forexample, there is one containing equal parts of the polymers andincluding anti-oxidants and dispersing agents, sold commercially underthe number 5011 by the Naugatuck Chemical Division of U. S. RubberCompany. A similar dispersion is sold under the name Hycar 0510 by theHycar Chemical Company. Other suitable copolymer dispersions have beenmade experimentally or are available commercially from these or othermanufactures- Many variations of our procedure will occur to thoseskilled in the art. The following examples of preferred embodiments ofthe invention may serve to explain the same more thoroughly. In theexamples, the aqueous dispersions referred to contain the usual amountof addition agents, such as anti-oxidants and dispersing agents.

Example I As the fibrous sheeting, there may be used, by way of example,a highly porous absorbent paper having a weight of the order of 27 lbs.,per ream of 480 sheets, 24" x 36" in size. The paper preferably shouldbe unsized and uncalendered and may have rugosities such as are obtainedby creping or embossing. While some wet strength may be desirable fromthe standpoint of handling the sheet during processing, it has beenfound that the best product results if paper having no initial wetstrength is used. For a web or sheet of the character mentioned,excellent results may be obtained using an impregnating bath containinga concentration of substantially 40 percent solids, including theaddition agents, and copolymers comprising by weight 39 to 50 percentstyrene and 50 to 61 percent butadiene. Variations in the amounts andtypes of vinyl copolymers are of course permissible as long as there ispresent a substantial amount, say, 35 percent styrene or substitutetherefor. The sheet is led through the impregnating bath, preferablywith a short flotation period preliminary to submersion. In its weakenedcondition the sheet should be subjected to no strain. On slow drying,conveniently done in a festoon drier at about 100 F., a product willresult having all of the excellent properties previously enumerated. Itis extremely well bonded internally and will permit the repeatedapplication and fast removal of normally tacky pressure-sensitiveadhesives without splitting or delamination.

Example II In this modification, the fibrous sheeting used was aporousMa'sslinn web, weighing 1.0 oz. per square yard which, in weight,is equivalent to paper of lbs. per ream of 480 sheets 24" 1:36" in size;The impregnant was loaded with a reinforcing carbon black to improve itsstrength characteristics. Carbon black may be used for this purpose withmuch satisfaction in amounts up to 60 percent of the solids content ofthe dispersion in instances where color is not a factor. The MasslinnWeb was led through the bath and then dried as in Example I. Thepreferred impregnant composition for a web of this character contains 48percent solids as follows:

Percent by weight Butadiene (48%)-styrene (52%) copolymer 75 ChannelBlack A suitable Channel Black is manufactured and sold in this countryby the Columbian Carbon Company under the designation D33.

As previously stated, the improved product does not necessitate the useof curing or vulcanizing steps, although some compounders may preferthem. Slightly higher tensile strength and better solvent resistance arethe resulting advantages, although the improved properties are obtainedat the expense of increased stifiness and increased processing timewhich results from the more complicated impregnant preparation and thein situ cure of the impregnant.

Where curing steps are desirable,'there may be added to the dispersion 1to 5 per cent each of zinc dibutyl dithiocarbamate, tetramethyl thiuramdisulfide and'sulfur based on the butadiene copolymer content of theimpregnant, or the same percentages of zinc dibutyl dithiocarbamate,zinc oxide and sulfur. Following drying, the sheet is cured for at leastone half hour at 250 F.

The invention has been described in its preferred form but manymodifications thereof are included within its spirit. It should beunderstood, therefore, that the invention is to be limited only by theprior art and the scope of the appended claims.

This application is a continuation of application Serial No. 556,494,filed September 29, 1944, and now aban doned.

What is claimed is:

l. A normally tacky and pressure-sensitive adhesive 'tape having aflexible, internally bonded paper backing comprising a thin web formedof paper fibers, originally having an open, highly porous structure, ofthe type conventionally employed in the formation of paper backedpressure-sensitive adhesive tapes, whose original flexibility, thinnessand weight are substantially those of a paper sheet of the order ofapproximately 27 lbs. per ream of 480 sheets 24 x 36" in size,additionally internally bonded by the bonding together of the fibersthereofby polymeric particles deposited in the formed web from anaqueous dispersion whose solids content is approximately to 60% of itsweight, said polymeric particles forming approximately to of the weightof said internally bonded web and consisting essentially of unvulcanizedparticles of a copolymer of butadiene and an initially unsaturatedcompound present in the copolymer to the extent of about 35 to by Weightthereof and selected from the group consisting of styrene, acrylicnitriles, isobutylene, and the methacrylates, and a normally tacky andpressure-sensitive adhesive united to said backing in manner such thatthe adhesive tape is removable from a suitable surface to which it isapplied without splitting, said internally bonded web having internalstrength sufficient to render it immune to splitting and delarninationwhen, in a roll of the tape, it is subjected to the forces exerted bythe adhesive of an overlying ply of the tape in the unwinding thereof,and being characterized by its ability to retain its internal andtensile strength and its flexibility upon exposure to temperaturesranging from at least the boiling point to at least the freezing pointof water.

2. A. normally tacky and pressure-sensitive adhesive tape, havingparticular utility as a masking tape, and according to claim 1, whereinthe thin web of paper fibers is uncalendered and has rugosities such asare obtained by creping.

3. A normally tacky and pressure-sensitive adhesive tape according toclaim 1, wherein the particles in the aqueous dispersion arepredominantly less than 4 microns in diameter.

4. A normally tacky and pressure-sensitive adhesive tape according toclaim 1, wherein the aqueous dispersion includes a proportion ofstrength imparting non-polymeric finely divided filler.

5. A normally tacky and pressure-sensitive adhesive tape according toclaim 1, wherein the aqueous dispersion includes a proportion ofstrength imparting finely divided carbon black.

- References Cited in the file of this patent UNITED STATES PATENTS1,958,821 Haarburger May 15, 1934 2,206,899 Kellgren July 9, 19402,335,124 Konrad Nov. 23, 1943 2,351,498 Fowler June 13, 1944 2,393,133White Jan. 15, 1946 2,416,232 Soday Feb. 18, 1947 2,424,923 Edgar et al.July 29, 1947 2,441,523 Ward May 11, 1948 2,447,538 Rust Aug. 24, 1948FOREIGN PATENTS 838,906 France Dec. 16, 1938 OTHER REFERENCES PaperTrade Journal, November 5, 1942.

1. A NORMALLY TACKY AND PRESSURE-SENSITIVE ADHESIVE TAPE HAVING AFLEXIBLE, INTERNALLY BONDED PAPER BACKING COMPRISING A THIN WEB FORMEDOF PAPER FIBERS, ORIGINALLY HAVING AN OPEN, HIGHLY POROUS STRUCTURE, OFTHE TYPE CONVENTIONALLY EMPLOYED IN THE FORMATION OF PAPER BACKEDPRESSURE-SENSITIVE ADHESIVE TAPES, WHOSE ORIGINAL FLEXIBILITY, THINNESSAND WEIGHT ARE SUBSTANTIALLY THOSE OF A PAPER SHEET OF THE ORDER OFAPPROXIMATELY 27 LBX. PER REAM OF 480 SHEETS 24" X 36" IN SIZE,ADDITIONALLY INTERNALLY BONDED BY THE BONDING TOGETHER OF THE FIBERSTHEREOF BY POLYMERIC PARTICLES DEPOSITED IN THE FORMED WEB FROM ANAQUEOUS DISPERSION WHOSE SOLIDS CONTENT IS APPROXIMATELY 30 TO 60% OFITS WEIGHT, SAID POLYMERIC PARTICLES FORMING APPROXIMATELY 40 TO 60% OFTHE WEIGHT OF SAID INTERNALLY BONDED WEB AND CONSISTING ESSENTIALLY OFUNVULCANIZED PARTICLES OF A COPOLYMER OF BUTADIENE AND AN INITIALLYUNSATURATED COMPOUND PRESENT IN THE COPOLYMER TO THE EXTENT OF ABOUT 35TO 70% BY WEIGHT THEREOF AND SELECTED FROM THE GROUP CONSISTING OFSTYRENE, ACRYLIC NITRILES, ISOBUTYLENE, AND THE METHACRYLATES, AND ANORMALLY TACKY AND PRESSURE-SENSITIVE ADHESIVE UNITED TO SAID BACKING INMANNER SUCH THAT THE ADHESIVE TAPE IS REMOVABLE FROM A SUITABLE SURFACETO WHICH IT IS APPLIED WITHOUT SPLITTING, SAID INTERNALLY BONDED WEBHAVING INTERANL STRENGTH SUFFICIENT TO RENDER IT IMMUNE TO SPLITTING ANDDELAMINATION WHEN, IN A ROLL OF THE TAPE, IT IS SUBJECTED TO THE FORCESEXERTED BY THE ADHESIVE OF AN OVERLYING PLY OF THE TAPE IN THE UNWINDINGTHEREOF, AND BEING CHARACTERIZED BY ITS ABILITY TO RETAIN ITS INTERNALAND TENSILE STRENGTH AND ITS FLEXIBILITY UPON EXPOSURE TO TEMPERATURERANGING FROM AT LEAST THE BOILING POINT TO AT LEAST THE FREEZING POINTOF WATER.